After-control signal detecting sensor for keyboard of electronic musical instrument

ABSTRACT

An after-control signal detecting sensor suitable for keyboard and particularly for pedal keyboard of electronic musical instrument. This sensor is connected to electric circuitry and comprises a flat-top elastic, flexible first conductive member having flexible first electrode and being positioned just below the row of keys for being depressed by them, a substantially triangular, apex-top flexible-elastic or rigid second conductive member having a second electrode and being positioned, at a distance, below said first conductive member when the first conductive member is in its non-depressed state, rendering the resistance between the electrodes infinite, an insulated open-top casing accommodating the aforesaid members therein, with the first conductive member being slidable in the opening of said casing, and a pair of pressor-stopper members on both sides of said second conductive member in said casing. Upon depression of key(s), the first conductive member is forced to deformably engage the second conductive member progressively, causing the resistance value to vary widely in accordance with the increase in the area of contact and with the increase in the amount of deformation of the conductive member(s). This variation of resistance is used to after-control tone color, tone volume, vibrato and other musical effects.

United States Patent [1 1 Kawamura Dec. 23, 1975 AFTER-CONTROL SIGNAL DETECTING SENSOR FOR KEYBOARD OF ELECTRONIC MUSICAL INSTRUMENT [75] Inventor: Kiyoshi Kawamura, Hamamatsu,

Japan [73] Assignee: Nippqp Gakki Semo' Kabushilti Kmsha, Japan [22] Filed: Dec. 26, I974 [2]]- Appl. N0.: 536,480

[30] Foreign Application Priority Data Dec. 28, 1973 Japan 49-4230 [52] US. Cl. 84/l.0l; 338/69; 84/D1G. 7; V 200/265 [51] Int. Cl. G101! 1/00 [58] Field of Search 338/69, 47, 96, 114; 8441.01, 1.17, 1.12, 1.24, 1.25, DIG. 7; 200/159 B [56] References Cited UNITED STATES PATENTS |,s47,u9 3/1932 Lertes et all 3411.11 x 2,036,691 4/1936 Gouror 84/117 X 2,141,231 12/1938 Trautwein 8411.24 X 2,340,213 1/1944 Ellsworth 84/D1G. 7 X 2,445,660 7/1948 Bruestle 338/114 2,848,020 8/1958 Lester 84/l.17 X

Primary Examiner-Joseph W. Hartary Assistant Examiner-U. Weldon Attorney, Agent, or Firm-Cushman, Darby & Cushman 1 1 ABSTRACT An after-control signal detecting sensor suitable for keyboard and particularly for pedal keyboard of electronic musical instrument. This sensor is connected to electric circuitry and comprises a flat-top elastic, flexible first conductive member having flexible first electrode and being positioned just below the row of keys for being depressed by them, a substantially triangular, apex-top flexible-elastic or rigid second conductive member having a second electrode and being positioned, at a distance, below said first conductive member when the first conductive member is in its non depressed state, rendering the resistance between the electrodes infinite, an.insulated open-top casing accommodating the aforesaid members therein, with the first conductive member being slidable in the opening of said casing, and a pair of pressor-stopper members on both sides of said second conductive member in said casing. Upon depression of key(s), the first eonductive member is forced to deformably engage the second conductive member progressively, causing the resistance value to vary widely in accordance with the increase in the area of contact and with the increase in the amount of deforman'on of the conductive member(s). This variation of resistance is used to aftercontrol tone color, tone volume, vibrato and other musical effects.

7Claims,9DrawingFlgures US. Patent Dec. 23, 1975 Sheet 1 of2 3,927,593

Kn PRIOR ART Kn PRIOR ART 4} r l V8 TM FIG. 6

US. Patent Dec. 23, 1975 Sheet20f2 3,927,593

22 KEYBOARD TONE TONE COLORING P GENERATOR KEYER FLTER EXPRESSION AMPLIFIER VIBRATO GENERATOR AFTER-CONTROL SIGNAL DETECTING SENSOR FOR KEYBOARD OF ELECTRONIC MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION a. Field of the invention The present invention pertains to after-control signal detecting sensor for keyboard, particularly for pedal keyboard of electronic musical instrument and is intended to perform after-control of various musical effects during the play of said musical instrument.

b. Description of the prior art Known means for after-controlling tone color, tone volume and such musical elTects as, for example, vibrato effect, for the keyboard electronic musical instrument are comprised of independent control devices having complicated variable resistance elements and being assigned exclusively for accomplishing the control of these effects. Besides, these devices are provided separately from the keyboard arrangement of the instrument. Therefore, the overall structure of the electronic musical instrument tends to become quite complicated, large and expensive. Moreover, those who can play a piano but have no experience in playing an electronic musical instrument find difficulty in playing on such complicated instrument.

In order to eliminate these drawbacks of known after-control devices, the inventor and an associate cooperated and have proposed an improved after-control signal detecting sensor means for keyboard arrangement of electronic musical instrument in the US. application Ser. No. 515,541 filed on Oct. 17, 1974. This prior sensor means comprises a conductive flexible first electrode, a conductive second electrode, and a conductive elastic member such as a conductive rubber interposed between the first and second electrodes and adhered thereto, and it is operative so that the conductive elastic member varies its resistance value according to the degree of compression and deformation of the conductive elastic member in proportion to the positions of the depressed keys. This variation of resistance is utilized for effecting after-control of the tone color, tone volume, vibrato and other such musical effects.

This prior sensing means is generally of the arrangement as illustrated in FIG. 1. More specifically, it comprises generally a flexible conductive pressure-transmitting member serving as a first electrode member 1, a rigid conductive base member serving as a second electrode member 2 and a conductive flexible and elastic member 3 sandwiched between the first and second electrode members for electrical conduction. This prior sensor means is operative so that, when any key K, is depressed to such a depth as will cause the compression and/or deformation of the conductive flexible and elastic member 3, the impedance of this member 3 varies from a certain initial resistance value R which may be several hundred kilo ohms and is exhibited when this member 3 is in the non-compressed, non-deformed state to a smaller value r such as several kilo ohms or several tens kilo ohms (r R) which is a level created in accordance with the position assumed by the depressed key. This variation of resistance is picked up and given off by the sensor means as an electric signal to be used as an after-control signal.

After a further research made by the inventor, it has been found that this prior sensor means having the aforesaid arrangement produces desirable effects in case it is provided as a relatively short length of the order of 200 mm. lt has been found, however, that when the sensor means disclosed in said United States Application having a length of 1000 mm or more is incorporated in an electronic musical instrument, the initial relatively great resistance value R which is expected to be possessed by the conductive flexible and elastic member becomes irregular, being locally in a lowered level before being deformed or compressed. This has been found by the author to be caused by the difficulty in manufacturing the conductive rubber to have a uniform resistance throughout its structure. Therefore, the said prior sensor means is not suitable for use in a lengthy structure. This sensor means has been found to have an initial resistance value R of several hundred kilo ohms and to vary in its resistance value to several kilo ohms to several tens kilo ohms depending on the degree of compression and deformation received by the conductive flexible member 3.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide an after-control signal detecting sensor for keyboard, particularly for pedalboard, of electronic musical instrument, which exhibits an extremely great initial resistance value when it is not depressed by a key and which can exhibit a wide range of variation of resistance when it is compressed and deformed by a key in accordance with the position of the depressed key.

Another object of the present invention is to provide a sensor of the type described, which performs aftercontrol of tone color, tone volume, vibrato and other such musical effects by a mere vertical movements of keys and which gives off a control signal corresponding to the depth of depression of keys.

Still another object of the present invention is to provide a sensor of the type described, which is simple in structure and cost saving.

These as well as other objects, features and advantages of the present invention will become apparent by reading the following detailed statement when taken in conjunction with the accompanying drawings.

BRIEF DESCRlPTlON OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of the arrangement of an example of the known after-control signal detecting sensor means for keyboard of an electronic musical instrument, to show the principle of the prior art.

FIG. 2 is an equivalent electric circuit diagram of the sensor means of H0. 1.

FIG. 3 is a fragmentary perspective view, partly broken away, of a preferred example of the after-control signal detecting sensor according to the present invention in relation to a corresponding foot pedal key.

FIG. 4 is a longitudinal sectional view, taken along the line IV-IV in FIG. 3, showing the normal state of the sensor wherein its first conductive member is held in spaced relation from the second conductive member when the sensor is not depressed by the key.

FIG. 5 is a cross sectional view of the same sensor taken along the line V-V in FIG. 4 to show the state when this sensor is not depressed by the key.

FIG. 6 is a similar view of the sensor of FIG. 5 in its operative state when the sensor is depressed by the key causing deformation in both the first and second conductive members thereby causing variation of the resistance value between the electrodes.

FIG. 7 is a block diagram of an example of an electronic musical instrument having a vibrato generator associated with the tone generator and operatively associated with the keyboard to show the arrangement of the aforesaid sensor of the present invention relative to the respective parts of the musical instrument.

FIG. 8 is a schematic electric circuit diagram of the vibrato generator circuit to be used in the electronic musical instrument of FIG. 7 embodying the present invention.

FIG. 9 is a fragmentary explanatory perspective view of a modified example of the sensor according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 3 through 6, there is shown an example of the after-control signal detecting sensor generally indicated at S for pedalboard arrangement of an electronic musical instrument, according to the present invention. This sensor comprises an electrically insulated, open-top casing generally indicated at 10; a flexible, elastic first conductive member 11 fitted slidably in the opening of the open-top casing 10 and having a flexible first electrode 14 and being capable of varying its electric resistance value in accordance with the amount of deformation and compression created by its corresponding depressed pedal key a flexible second conductive member 12 having a generally triangular cross section and being secured on the bottom of said casing in such a way that its apex is positioned in spaced relation from the bottom surface of the first conductive member and being capable of varying its electric resistance value in accordance with the amount of deformation caused by being contacted by the first conductive member when the latter is depressed; and a pair of electrically insulated pressor-stopper members 13 and 13 supported on the inside of said casing 10 at both sides of said second conductive member between the two conductive members 11 and 12,

The first conductive member 11 has a flat upper surface 11a and a substantially flat bottom surface 11b which is substantially parallel with the upper flat surface lla. This first conductive member 11 is made of, for example, a foamed conductive rubber such as foamed butadiene rubber or other porous conductive material intennixed with conductive particles, for example, carbon black particles (40-60 wt.%) and has the characteristic that its electrical resistance value is varied in accordance with the degree of its deformation and compression caused by an external force and with the amount of contact with the second conductive member 12.

The first electrode 14 which is embedded in the first conductive member 11 close to the upper surface thereof is made of a tough but easily flexible flatly woven conductive metal wire such as tin-plated net-like copper wire or a conductive thin metal plate or made of a conductive natural rubber or a conductive synthetic rubber of ribbon shape as is those disclosed in the aforesaid US. application Ser. No. 515,541. This first electrode 14 may be adhered to the upper surface of the first conductive member 11 by an appropriate adhesive. In this example, the first electrode 14 is molded integrally with the first conductive member 11 so that the rubber of the first conductive member enters into 4 the meshes of the woven net-like electrode structure at the time of molding. This molding serves to strengthening both chemical and physical relative bonding of the rubber and the electrode.

The second conductive member 12 is of a generally triangular cross section so that it has an upwardly extending protrusion as shown in FIGS. 5 and 3 and is made of material similar to that of the first conductive member ll and has the characteristic same as that of the first conductive member.

The second electrode 15 is made of a tough conductive material similar to that of the first electrode 14 but it requires no flexibility and it is embedded, by molding, in the second conductive member 12 close to the bottom thereof, or it is adhered to the bottom of the second conductive member by an appropriate adhesive. Because of the fact that this second electrode 15 is not required to have flexibility, it is only enough that this second electrode 15 is tightly adhered to the rubber of the second conductive member 12 for electric conductron.

As shown, the second conductive member 12 having the second electrode 15 therein is fixed at its bottom to the upper surface of the bottom wall 10a of the casing 10 in such a way that the apex of the protrusion 12a is positioned below the bottom surface 11b of the first conductive member 11 leaving a gap G between the bottom surface of the first conductive member 11 and this apex in the nonnal state of these first and second conductive members 11 and 12 wherein the first conductive member 1 l is not depressed by a foot pedal key P In such a state of these two members 1 l and 12, the resistance between the two electrodes 14 and 15 remains substantially infinite in value.

The pressor-stopper members 13 and 13 forming a pair are each of a substantially round cross section and are each comprised of a relatively hard but somewhat flexible non-conductive rubber such as non-conductive butadiene rubber. These members 13 and 13 serve as a stopper means to keep the bottom surface 11b of the first conductive member 11 from contacting the apex of the protrusion 12a of the second conductive member 12 in the normal state of the sensor S.

The flat, flexible, elastic first conductive member 11 in this example is of a breadth slightly greater than the breadth of the opening of the casing 10 so that the edges of this opening slightly bite into the conductive member 11 to establish friction-contact therebetween. This arrangement will prevent casual slip-out of the pressor-stopper members 13 and 13 from the opening of the casing 10.

The casing 10 in this example is made of a molded electrically insulated synthetic resin and is structured so that it has a flat base wall 10a, two spaced holding walls 10b and 10b extending from the base wall 10a forming therein a hollow region having a bilaterally outwardly bulging cross section as shown in FIG. 5, thus providing spaces G" and G" on both sides of that lower portion of the first conductive member ll relative to the inner wall surfaces of the bulging portions of the respective walls 10b and 10b.

The first and second conductive members 11 and 12 and the pressor-stopper members 13 and 13 are accommodated in the hollow region defined by the holding walls 10b, 10b and the base wall 100.

The flexible, elastic first conductive member 11 in this example is prepared to have such a size as is slightly greater than the size of the opening of the open-top casing but to be able to frictionally and slidably move into the casing 10 when depressed by a pedal key P, while filling the spaces G" and G" and to recover its initial position at which its about one half portion projects beyond the edge of the said opening when this conductive member 11 is not in its deformed and compressed state. The second conductive member 12 is fixed to the base wall 10a of the casing. The pressorstopper members 13 and 13 are in contact with the inner surfaces of the holding walls 10b and 10b of the casing, forming said gap G between the two conductive members 11 and 12 to support the first conductive member 11 above the second conductive member 12 leaving said gap G therebetween. Thus, in the state that there is no external force applied to the first conductive member 11, the first electrode 14 is insulated completely from the second electrode 15, and accordingly, the initial resistance between these electrodes is substantially infinite.

With the foregoing arrangement of the sensor S of the present invention, when the upper surface Ila of the first conductive member carrying the first electrode 14 therein is pressed vertically downwardly from thereabove by, for example, an actuator not shown of a foot pedal key P or directly by this foot pedal key with a force between about 60 g and 1 kg to such an extent as will cause the first conductive member 11 to move downwardly to be received for any desired distance in the casing 10, the bottom surface 11b of the first conductive member 11 will eventually be brought into contact with the apex of the protrusion 12a of the second conductive member 12 carrying the second electrode 15 therein. Thereafter, as this first conductive member 11 is pressed with an increasing force such as more than 1 kg, the bottom surface llb will be brought progressively into pressure engagement not only with the protrusion 12a but also with the pressor-stopper members 13 and 13 so that these latter, in turn, will press the protrusion 12a at both inclined sides of the triangular shaped second conductive member 12, forcing the protrusion 12a to deform upwardly further to establish further progressive pressure engagement with the first conductive member 11. With such relative progressive movements of these two conductive members l1 and 12, it should be noted that at the time the bottom of the first conductive member 11 lightly touches the apex of the protrusion [22 of the second conductive member 12, there still is present the socalled non-sensitive period". However, as the area of contact between these conductive members progressively increases in accordance with the increasing force applied externally to the first conductive member 1 l by the foot pedal key P,,, the conductive particles or metal dust located in the compressed, deformed regions of the conductive members 11 and 12 are caused to gather in these regions densely, and these regions of the conductive members 11 and 12 will exhibit a resistance value r which, prior to the contact of these conductive members, was almost infinite now varies progressively to a much smaller level r R of for example, several kilo ohms or several tens kilo ohms, depending on the amount of contact of the two conductive members and also on the amount of deformation-compression of these members. The signal representing this varied resistance is inputted into, for example, a tone coloring filter of the electronic musical instrument arranged as, for example, shown in FIGS. 7 and 8.

In the preferred example described, the second conductive member 12 has a generally triangular cross section and this shape is advantageous in that the area of contact between the first and second conductive members 11 and12 starts with a small amount when the first conductive member 11 is brought initially into light contact with the apex of the protrusion 12a of the second conductive member 12, and that thereafter, as the first conductive member 11 is pressed further with a progressively greater force, this area of contact and the relative compression and deformation of the two conductive members will increase progressively accordingly. Furthermore, as the triangular shape of the second conductive member 12 is pressed progressively against its lateral sides by the relatively hard pressorstopper members, the bilateral surfaces of the conductive member 12 will become concaved and the protrusion 12a will deform upwardly progressively into the first conductivemember 11.

Thus, there will arise a decrease in the resistance value in each of the compressed and deformed first and second conductive members 11 and 12. With the multiplied effect brought about by the decrease in resistance of these two conductive members 11 and 12, there can be obtained a very wide range of variation of after-control signal. Such variations will be obtained for the respective foot pedal depressing operations.

The above-mentioned after-control detecting sensor arrangement is especially suitable for use in a pedal keyboard and description has been made on the instance that the after-control signal detecting sensor is applied to a pedal keyboard arrangement in an electronic musical instrument. It should be noted, however, that this sensor may be used equally effectively also for manual keyboard arrangement of the instrument especially where a long sensor is required.

Referring now to FIG. 7, there is shown a block diagram of an example of a whole system of electronic musical instrument to which the after-control signal detecting sensor of the present invention is applicable. This electronic musical instrument, in general, is of the type having a tone generator circuit 21, a keyboard arrangement 22, a keyer circuit 23, a tone coloring filter circuit 24, an expression circuit 25, an amplifier circuit 27, a loud-speaker 28, and a vibrato generator circuit 29 which are all of the known parts in the art except for the keyboard arrangement according to the present invention, and these parts are connected in the order as shown in FIG. 7.

FIG. 8 shows a schematic electric circuit diagram of the vibrato generator circuit 29 to be used in the electronic musical instrument of FIG. 7.

The vibrato generator circuit 29 is of the type having a transistor and capacitors, a resistor R for deriving the output signal, and a specifically arranged variable impedance or resistor VR, i.e., an after-control signal detecting sensor according to the present invention, which has been explained above in detail. It should be understood that in FIG. 8 this variable resistor VR is shown just for mentioning the principle.

FIG. 9 shows a modification of the after-control signal detecting sensor of the present invention. In this example, the casing 10' is of the structure comprising a flat base wall and two spaced holding walls 10b and 10b extending from this base wall 100, each of said holding walls having a shoulder 13' formed at an appropriate site on the inner side of the wall. These shoulders 13 and 13' serve as the stopper-pressor for the first conductive member 11' as in the preceding example. A flexible, elastic first conductive member 11' carrying a flexible first electrode embedded in the upper end portion thereof is snugly and slidably received in the opening defined by the two opposing holding walls 10b and 10b and supported at its own stepped portions on the respective shoulders 13' and 13' of these holding walls. A flexible second conductive member 12 carrying a second electrode embedded in its base is fixed on the base wall 100' of the casing 10' in a manner similar to the preceding example. This second conductive member 12' is of a generally triangular cross section with its apex facing the bottom of the first conductive member 11' with a gap G present therebetween.

Upon application of a force from above the first conductive member 11' by, for example, a pedal key P as in the preceding example, the first conductive member 11' will become compressed and deformed so that the bottom of this first conductive member will progressively engage the apex and then the inclined side surfaces of the second conductive member 12' in the same way as described in connection with the preceding example. Thus, the similar after-control effects can be obtained.

Such sensor as has been described above is positioned at a distance below the keys and extends in transverse direction of the keys in such a manner that the first electrode 14 (14') faces the bottom of each corresponding key.

The first conductive member 11 (11) may have a coarse bottom surface and the second conductive member 12 (12') may also have coarse lateral surfaces so that the contact area produced by these surfaces will be all the more increased.

The second conductive member 12 (12') may not be flexible, and its conductive rubber may be a relatively hard one.

Various other modifications will be conceived by those skilled in the art without departing from the scope of the appended claims.

According to the present invention, there is provided an after-control signal detecting sensor which features in that it can be provided as a long sensor suitable for the keyboard of an electronic musical instrument because of its arrangement that the flexible, elastic first conductive member having therein a flexible first electrode is positioned above the flexible or less flexible second conductive member, with a gap G (G') therebetween when the first conductive member is not pressed by a key. Thus, it is possible to keep the initial resistance of these conductive members almost infinite, whereby wide range of variation of resistance can be obtained in accordance with the amount of compression, deformation and contact of these two conductive members.

The triangular shape of the second conductive member is useful in that the area of contact with the first conductive member can vary in a progressive manner.

Moreover, the inclined side surfaces of the triangular second conductive member can deform in case it is made with a flexible rubber by the action of the pressor-stopper members, to contribute to further wide variations of resistance.

I claim:

1. An after-control signal detecting sensor positioned at a distance below keyboard of an electronic musical instrument to correspond to the respective depressable keys and connected to a circuit of said musical instrument, comprising:

an electrically insulated open-top casing having a bottom wall and opposing holding side walls extending from said bottom wall,

a flexible, elastic first conductive member slidably fitted in the opening of said casing and having a flexible first electrode and capable of varying its resistance in accordance with its compression and deformation caused when pressed by each key,

a second conductive member having a second electrode and being supported on the bottom wall of said casing therein and separated with a gap from said first conductive member in the non-compressed normal state of the first conductive member, said first conductive member being brought into area contact with said second conductive member under forces applied by each key depressed, and electrically insulated pressor-stopper members provided inside said casing at opposite sides of the second conductive member and so positioned as to maintain said gap between the first and second conductive members in said non-compressed normal state of the first conductive member.

2. An after-control signal detecting sensor according to claim 1, in which said second conductive member is flexible and elastic.

3. An after-control signal detecting sensor according to claim 2, in which said first and second conductive members are made with a material selected from foamed conductive rubber and porous conductive ma terial, said first electrode is made with a flexible conductive material selected from conductive natural rubber, conductive synthetic rubber, flexible conductive thin metal plate and woven tin-plated copper wire; and said second electrode is made with conductive material similar to that of said first electrode but requiring no flexibility.

4. An after-control signal detecting sensor according to claim 2, in which said second conductive member has a substantially triangular cross section with its apex facing the bottom of the first conductive member, said apex being positioned at a distance from the bottom of the first conductive member when the first conductive member is not depressed by an external force.

5. An after-control signal detecting sensor according to claim 2, in which said insulated pressor-stopper members are made with a relatively rigid material selected from natural rubber and synthetic rubber and each has a substantially round cross section.

6. An aftercontrol signal detecting sensor according to claim 4, in which said first conductive member has a coarse bottom surface and said second conductive member has coarse inclined surfaces.

7. An after-control signal detecting sensor according to claim 2, in which the sensor has a length of 1,000

mm or longer. 

1. An after-control signal detecting sensor positioned at a distance below keyboard of an electronic musical instrument to correspond to the respective depressable keys and connected to a circuit of said musical instrument, comprising: an electrically insulated open-top casing having a bottom wall and opposing holding side walls extending from said bottom wall, a flexible, elastic first conductive member slidably fitted in the opening of said casing and having a flexible first electrode and capable of varying its resistance in accordance with its compression and deformation caused when pressed by each key, a second conductive member having a second electrode and being supported on the bottom wall of said casing therein and separated with a gap from said first conductive member in the non-compressed normal state of the first conductive member, said first conductive member being brought into area contact with said second conductive member under forces applied by each key depressed, and electrically insulated pressor-stopper members provided inside said casing at opposite sides of the second conductive member and so positioned as to maintain said gap between the first and second conductive members in said non-compressed normal state of the first conductive member.
 2. An after-control signal detecting sensor according to claim 1, in which said second conductive member is flexible and elastic.
 3. An after-control signal detecting sensor according to claim 2, in which said first and second conductive members are made with a material selected from foamed conductive rubber and porous conductive material, said first electrode is made with a flexible conductive material selected from conductive natural rubbeR, conductive synthetic rubber, flexible conductive thin metal plate and woven tin-plated copper wire; and said second electrode is made with conductive material similar to that of said first electrode but requiring no flexibility.
 4. An after-control signal detecting sensor according to claim 2, in which said second conductive member has a substantially triangular cross section with its apex facing the bottom of the first conductive member, said apex being positioned at a distance from the bottom of the first conductive member when the first conductive member is not depressed by an external force.
 5. An after-control signal detecting sensor according to claim 2, in which said insulated pressor-stopper members are made with a relatively rigid material selected from natural rubber and synthetic rubber and each has a substantially round cross section.
 6. An after-control signal detecting sensor according to claim 4, in which said first conductive member has a coarse bottom surface and said second conductive member has coarse inclined surfaces.
 7. An after-control signal detecting sensor according to claim 2, in which the sensor has a length of 1,000 mm or longer. 